Many optical fiber systems include one or more fiber amplifiers disposed along the fiber path between the transmitter and the receiver to boost the strength of the optical signal and overcome losses in the fiber system, such as fiber transmission losses, coupling losses and the like. Fiber amplifiers are energized by light from one or more pump lasers coupled into the fiber system. It is often desirable to combine the pump light of two or more pump lasers into a single fiber in order to increase the pump power reaching the fiber amplifier. Higher pump power results in higher amplifier gain, and thus reduces the number of amplifiers that need to be disposed along the fiber path. The amplifier noise may also be reduced. Different types of fiber amplifiers require pump lasers operating at different wavelengths. For example, an erbium fiber amplifier typically requires a pump laser operating at about 980 nm and a fiber Raman amplifier for amplifiying light at about 1550 nm requires a pump laser wavelength of about 1460 nm. In some situations, it is also desireable to combine pump lasers of different wavelengths. For example, when pumping a Raman amplifier, it may be useful to pump two or more different wavelengths in order to control the gain spectrum for the signal light.
Prior solutions to combining the output power from pump lasers have employed the use of a 50/50 splitter, which is lossy. Other solutions have included polarization combining the output from two lasers, which requires the use of a polarizer. However, there are problems with currently available optical configurations used for polarization combining. For example, Wollaston polarizing beamsplitters are expensive and difficult to align. On the other hand, thin film polarizers such as polarizing beamsplitter cubes operate with large angular separation between the p- and s-polarized beams, which makes operation in compact, in-line packages difficult.
Therefore, there is a need to develop a compact, in-line polarization combiner that is straightforward to align.